The need to provide an adequate ammunition capacity is always a consideration with autoloading firearms. This consideration is particularly important with firearms intended for use in military or law-enforcement applications, especially where the firearm is capable of full-automatic fire. Cartridge magazines of limited capacity may have to be changed or reloaded too frequently for effectiveness or safety in combat applications, and may also further burden the shooter who must carry additional magazines necessary for the desired number of rounds.
Detachable cartridge magazines generally take the form either of a box magazine, in which the rounds are held and fed in a straight or staggered line; or a drum magazine in which the rounds are held and fed on a generally circular or spiral path. Although each kind of magazine has certain advantages and disadvantages, a drum magazine generally can be designed to hold and effectively feed more rounds than a box magazine, other factors being equal.
Notwithstanding the foregoing, a box magazine can provide desired round-holding capacity for many applications, particularly for smaller-caliber firearms where box magazines holding twenty or even thirty rounds can be built without undue length or feeding problems during automatic firing. With larger-caliber firearms, the physical size and weight of cartridges make box magazines impractical for more than about ten rounds. This problem is especially acute in the case of assault shotguns such as disclosed in copending patent application Ser. No. 336,328 filed Dec. 31, 1981, where the assault shotgun is intended for military or other combat applications and may be selectively capable of full-automatic firing.
Although drum magazines are known in the art, existing drum magazine designs generally have various disadvantages which may become more pronounced if these designs are adapted for loading and feeding shotgun shells. For example, prior-art drum magazines tend to be relatively heavy even when empty, and become correspondingly heavier when fully loaded with relatively heavy ammunition such as shotgun shells. Moreover, some drum magazines are difficult to reload without removing the drum cover or lid, an operation which is not recommended for loading in the field. Moreover, drum magazines of the prior art sometimes are less dependable in feeding rounds to a firearm under full-automatic fire, especially where the relative size and mass of shotgun shells is considered. This problem is compounded by the fact that the overall length of shotgun shells of a given size, e.g., twelve gauge, varies depending on factors such as the load of the shell. An effective drum magazine for a particular firearm should be capable of loading and feeding the various kinds of shells for which the firearm is chambered.